INCOME TAXES - Effective Income Tax Reconciliation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Amount
U.S. Federal income tax expense	$ 625	$ 273	$ 473
Increase (decrease) resulting from:
State and local income taxes (net of federal benefit)	126	54	73
Bank-owned life insurance	(14)	(12)	(12)
Tax-exempt interest	(7)	(10)	(15)
Tax advantaged investments (including related credits)	(95)	(68)	(50)
Other tax credits	(7)	(6)	(10)
Adjustments for uncertain tax positions	3	(1)	0
Non-deductible FDIC premiums	14	14	13
Legacy tax matters	0	(4)	(19)
Other	13	1	7
Income tax expense	$ 658	$ 241	$ 460
Rate
U.S. Federal income tax rate	21.00%	21.00%	21.00%
Increase (decrease) resulting from:
State and local income taxes (net of federal benefit)	4.20%	4.20%	3.20%
Bank-owned life insurance	(0.50%)	(0.90%)	(0.50%)
Tax-exempt interest	(0.20%)	(0.70%)	(0.70%)
Tax advantaged investments (including related credits)	(3.20%)	(5.30%)	(2.30%)
Other tax credits	(0.20%)	(0.50%)	(0.40%)
Adjustments for uncertain tax positions	0.10%	(0.10%)	0.00%
Non-deductible FDIC premiums	0.50%	1.10%	0.60%
Legacy tax matters	0.00%	(0.30%)	(0.80%)
Other	0.40%	0.00%	0.30%
Total income tax expense and tax rate	22.10%	18.50%	20.40%